This invention relates to an improved method of preparation of fluorocompounds. More particularly, the invention relates to use of heat and vacuum to remove impurities and adding an emulsifier to the fluorocarbon compound mass to create a concentrated liquid rather than a tacky solid product.
In recent years it has become increasingly popular to sell carpets that have been treated to resist soiling. These soil-resisting treatment products are bought by the carpet manufacturers as aqueous emulsions and are applied to the carpets by spraying as the final step in carpet manufacturing. As a result, the treatment is confined to the carpet face with fiber surfaces deep in the pile being unprotected. The face fibers are essentially sheathed with antisoiling agent but, since there is no means of binding the modifier to the fiber surface, as the surfaces are subjected to normal wear the sheath is slowly lost by abrasion.
It was discovered that the surface of Nylon 6 fibers can be altered prior to sale to a carpet manufacturer by using a properly designed fluorocarbon containing compound. The low surface energy fiber is essentially unaffected by the subsequent carpet manufacturing steps and results in an antisoiling carpet in which the complete pile is treated, not just the carpet face. This novel technology allows the fiber manufacturer complete control of the surface modification and eliminates the additional operation in the carpet manufacturer's plant.
The tetra ester of pyromellitic acid is such a fluorocarbon containing compound. See U.S. allowed Ser. No. 861,372, filed Dec. 16, 1977, now U.S. Pat. No. 4,209,610 in which two of the esters contain perfluoroalkylethyl chains and the other two contain 2-hydroxy-3-chloropropyl groups. The preferred compound is a 50--50 mixture of two isomers and hereafter will be referred to as DSR which has the following structure: ##STR1##
The low surface energies needed to produce a soil-repellent surface, one not wetted by either water or oil-borne stains, dictates that the surface consist of oriented fluorocarbon chains. Commercially, the fluorocarbon chains are synthesized by the telomerization of pentafluoroethyliodide and tetrafluoroethylene. The desired telomers are separated by distillation from the telomer mixture. The lower molecular weight telomers are recycled and the very small amount of higher telomers are either discarded or used for other purposes. Perfluoroalkylethanol is produced by addition of ethylene and then conversion of the perfluoroalkylethyliodide to the alcohol. Thus, steps of the laboratory synthesis are, EQU 1. R.sub.F I+CH.sub.2 =CH.fwdarw.R.sub.F CH.sub.2 CH.sub.2 I EQU 2. R.sub.F CH.sub.2 CH.sub.2 I.fwdarw.R.sub.F CH.sub.2 CH.sub.2 OH
where R.sub.F =CF.sub.2 CF.sub.2 (CF.sub.2 CF.sub.2).sub.n n=2,3,4 and 5, ##STR2## Two moles of the perfluoroalkylethanol are reacted with pyromellitic dianhydride by stirring in dimethylformamide (DMF) solution for twenty-four hours at 45.degree. C. To the solution of the intermediate, diester-diacid, was added three moles of epichlorohydrin and three mole percent triethylamine based on the number of moles of carboxyl groups present. The temperature is raised to 60.degree. C. and the reaction, which is complete in six to eight hours, is followed by titration of the excess epichlorohydrin with hydrogen bromide in glacial acetic acid. The reaction mixture contains about 50 percent DSR which is recovered by drowning in fifteen to twenty volumes of cold (.about.5.degree. C.) water with rapid stirring. The soft particles are washed five times with equivalent volumes of cold water to remove the solvent and the epichlorohydrin. The last wash slurry is pumped to a filter. The soft tacky filter cake contains an equal weight of water and is difficult to manually transfer to drums for shipping in large quantities.
In the development of a commercial process for manufacturing DSR, a change was made in the reaction solvent from dimethylformamide (DMF) to N-methylpyrrolidone (NMP). See U.S. Ser. No. 044,880 filed June 6, 1979, hereby incorporated by reference. Analysis indicates a purer product which is reflected in greater laundry stability.